The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
The present invention relates to hyperbranched polyimides.
Aromatic polyimides (PIs) are well known, high-performance materials with widespread applications in the aerospace and electronics industries due to their excellent thermomechanical and dielectric properties. Recently, it was demonstrated that they are useful as optical materials based on their optical anisotropy when cast in directions parallel (in-plane) and perpendicular (out-of-plane) to the film surface. However, when fully imidized, most aromatic PI""s have limited solubility in common organic solvents, thus restricting the choice in processing options. Numerous research efforts have focused on organo-soluble PIs from the modification of the structure without substantially decreasing rigidity of their backbone. Solubility is desired in order to allow processing polymers with preformed imide units and to avoid the problems associated with handling poly(amic acid) (PAA) precursors. In addition, homogeneous, post-polymer reactions of soluble aromatic polyimides would allow better control in the introduction of desirable functional groups.
A viable alternative to attaining solubility in aromatic PIs is to change the traditional, linear geometry of the macromolecules to three-dimensional, highly branched (dendritic) architecture. As a subset of dendritic polymers, hyperbranched polymers have several important advantages such as better solubility compared to their linear counterparts, and easier synthesis than their analogous dendrimers, which involve tedious multi-step synthesis. Large quantity of hyperbranched polymers can be easily produced from ABx (xxe2x89xa72) monomers. There are few reports on synthesis of hyperbranched PIs, and their utilization.
Accordingly, it is an object of the present invention to provide new hyperbranched polyimides.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the present invention there are provided new hyperbranched polymers having repeating units of the formula 
The polymer is prepared by the polymerization of the AB2 monomer N-{3,5-bis(4-hydroxybenzoyl)benzene}-4-fluoroisophthalimide.
Synthesis of the AB2 monomer, N-{3,5-bis(4-hydroxybenzoyl)benzene}-4-fluoroisophthalimide, is shown by the following reaction sequence: 
In this sequence, 5-nitroisophthalic acid is first treated with thionyl chloride (reaction a) to provide 5-nitroisophthaloyl dichloride (1). Friedel-Crafts reaction of 1 with anisole in the presence of aluminum chloride (reaction b) gives 3,5-bis(4-methoxybenzoyl)nitrobenzene (2), which is then demethylated with pyridine hydrochloride (reaction c) to provide 3,5-bis(4-hydroxybenzoyl)nitrobenzene (3). Compound 3 is then reduced (reaction d) to 3,5-bis(4-hydroxybenzoyl)aniline (4). Upon reacting with 4-fluoroisophthalic anhydride, with catalytic amount of isoquinoline, 4 is converted to the monomer 5, N-{3,5-bis(4-hydroxybenzoyl)benzene}-4-fluoroisophthalimide (reaction e).
The resulting AB2 monomer can be polymerized in the presence of potassium carbonate under Dean-Stark conditions to afford high molecular, low viscosity hyperbranched ether-ketone-imide polymer having repeating units with hydroxyl endgroups: 
These endgroups can be readily converted to other useful and thermally reactive groups, such as, for example, xe2x80x94CH2xe2x80x94CHxe2x95x90CH2, xe2x80x94CH2xe2x80x94Cxe2x89xa1CH and 
The polymers with reactive endgroups are key components of high-temperature matrix resins such as cyanate ester resins, phthalonitrile- and benzoxazine-based thermosets, and the like.